System and use concerning under water eddy current measurements on components for nuclear reactors

Abstract

The invention concerns a system suited for carrying out eddy current measurements on components for nuclear reactors when these components are located in water. The system comprises a control unit, a measurement probe and a first cable suited to constitute at least a part of the connection between the control unit and the measurement probe. The system also comprises a switching unit, suited to be located in water and arranged to be connected with said first cable, and to be connected with the measurement probe. The switching unit has a switching device which can assume at least a first and a second state. In the first state, the first cable is connected with the measurement probe. In the second state, the first cable is not connected with the measurement probe. The invention also concerns the use of the system.

1. A system for carrying out eddy current measurements on components for nuclear reactors when these components are located in water, wherein the system is adapted to measure at least one property of these components, such as the thickness of at least one layer located on the component, by generating at least one electromagnetic alternating field which penetrates the component in question and in the same generates eddy currents which retroact on the generated electromagnetic alternating field, wherein the system is arranged to carry out the measurement of the property in question by measuring a response to the generated electromagnetic alternating field and carrying out a calculation of the property in question, wherein the system comprises,
 a control unit located outside of the water and arranged to control the measurement, 
 a measurement probe moved to the immediate vicinity of the components in the water, wherein the measurement probe comprises means, preferably at least one coil, with the help of which the electromagnetic alternating field which penetrates the component in question is generated, 
 a first cable constituting at least a part of the connection between the control unit and the measurement probe, wherein this cable is at least partially located in the water, and 
 a switching unit located in the water and arranged to be connected with said first cable, and to be connected with the measurement probe, wherein the switching unit comprises a switching device which can assume at least a first and a second state, wherein in the first state the first cable is connected with the measurement probe and in the second state the first cable is not connected with the measurement probe. 
 
     
     
       2. A system according to  claim 1 , wherein the switching unit comprises at least a first known load and is arranged such that in said second state the first cable is connected with the first known load. 
     
     
       3. A system according to  claim 2 , wherein the first known load has a known finite impedance value. 
     
     
       4. A system according to  claim 3 , wherein the known finite impedance value is between 5 Ω and 1000 Ω. 
     
     
       5. A system according to  claim 2 , wherein the switching unit comprises a second known load, the switching device can assume a third state, and wherein in the third state the first cable is connected with the second known load. 
     
     
       6. A system according to  claim 5 , wherein the second known load has essentially the impedance value 0 Ω. 
     
     
       7. A system according to  claim 5 , wherein the switching unit comprises a third known load, wherein the switching device can assume a fourth state, wherein in the fourth state the first cable is connected with the third known load. 
     
     
       8. A system according to  claim 7 , wherein the third known load has essentially infinite impedance value. 
     
     
       9. A system according to  claim 1 , comprising a second cable, of a certain length I, wherein one end of the second cable is connected to the switching unit and the other end of the second cable is connected to the measurement probe, wherein in the first state the first cable is connected with the measurement probe via the second cable. 
     
     
       10. A system according to  claim 9 , wherein the switching unit comprises a third cable, with the same, or at least essentially the same, characteristics as the second cable, wherein the switching device is arranged such that the first cable can be connected to the third cable instead of to the second cable. 
     
     
       11. A system according to  claim 10 , wherein the third cable has exactly, or at least approximately, the length I. 
     
     
       12. A system according to  claim 10 , wherein the switching unit is arranged such that in one, two or all of said second, third and fourth states, the first cable is connected with the known load via the third cable. 
     
     
       13. A system according to  claim 1 , wherein the switching unit has a casing which is constructed not to let in water, such that the parts which are arranged within the casing remain dry when the switching unit is used in water. 
     
     
       14. A system according to  claim 13 , arranged with means for introducing a gas, preferably air, within the casing when the system is used and the switching unit is located in water, for causing an overpressure within the casing such that water is prevented from penetrating into the inside of the casing. 
     
     
       15. A system according  claim 1 , comprising a measurement probe holder which is arranged to be able to move the measurement probe to and from the component on which it is to be measured. 
     
     
       16. A system according to  claim 15 , comprising one or more calibration objects, with known properties, located in the vicinity of the measurement probe holder, wherein the measurement probe holder is arranged to be able to move the measurement probe to said one or more calibration objects for enabling a calibration measurement. 
     
     
       17. A system according to  claim 15 , comprising remote control means arranged to enable remote control of the movement of the measurement probe holder. 
     
     
       18. A system according to  claim 1 , comprising a temperature sensor which is adapted to be located next to or in the vicinity of the switching unit or the measurement probe and which communicates with the control unit. 
     
     
       19. A system according to  claim 1 , comprising a resistance meter, intended to be located outside of the water, and adapted to carry out measurement of direct current resistance, wherein said resistance meter is adapted to be connected with one end of said first cable at the same time as the second end of the first cable is connected to the switching unit. 
     
     
       20. A system according to  claim 1 , wherein the switching unit and the parts which form part thereof are adapted to function in a radioactive environment of the kind which may be the case during measurement in water on components for nuclear reactors. 
     
     
       21. A system according to  claim 1 , comprising a further measurement probe adapted to be connected with the switching unit at the same time as the previously mentioned measurement probe is connected to the switching unit. 
     
     
       22. A method comprising:
 providing the system according to  claim 1 , 
 carrying out the measurements on said components which are fuel rods for a nuclear reactor. 
 
     
     
       23. The method of  claim 22  further comprising:
 measuring the thickness of at least one layer on the fuel rods. 
 
     
     
       24. The method of  claim 22  further comprising:
 measuring the hydride content in the fuel rods. 
 
     
     
       25. The method of  claim 22  further comprising:
 carrying out the measurements when the fuel rods are located in a water pool.